The fabrication of multi-layered plastic articles in which the layers are bonded together produces a stiff article of a greater rigidity than can be achieved with a single sheet. However, any deficiency in the bond between the layers or shells results in a loss of strength in the laminate article. Thus, it is important to have shells which mate perfectly at their interface so that the bonding can be across the entire interface. In fabricating male and female moulds extreme accuracy is, therefore, required to match the mould surfaces. For parts having complex surfaces such accuracy is difficult to achieve. Elaborate jigs and measurement techniques are required when the moulds are to be fabricated manually. If computer controlled machines are used then the cost of these machines represents a significant expense.
Accordingly, it is an object of the invention to provide an improved method of fabricating thermoformed plastic articles. It is a further object of the invention to provide a method of producing male and female moulds with interface surfaces formed with a high degree of accuracy.